This invention relates to protective monitors or controls, and particularly to monitors or controls for protecting compressors in air conditioning units.
Loads such as motors in air conditioning units, especially air conditioning compressors, may draw excessive currents and overheat during operation. To protect the compressor and the unit from the effects of overheating, a thermal protective device in the unit may cut off further flow to the compressor. The protective sensor device later allows current to the unit to resume. However, the thermal protective sensor often allows current to restart before the unit has actually recovered from its overloaded condition. Then the thermal protective device again cuts off current. This cut off and resumption of current may recycle many times before system operates normally. Repeated cycling shortens the life of the sensor contacts as well as the compressor.
An object of the invention is to overcome these difficulties.
According to an embodiment of the invention, a thermal protector opens in response to excess current or heat and a delay defers resumption of current flow through the thermal protector by a period that extends beyond the expected current resumption.
According to an embodiment a reset relay responds to the delay to maintain the off condition during an adjustable period.
According to an embodiment this is accomplished by an arrangement external to the unit.
The various features that characterize the invention are pointed out in the claims forming a part of this specification. Other objects and advantages of the invention will become evident from the following detailed description when read in light of the following drawings.